1. Technical Field
The present invention relates generally to an improved method to manage logical volumes and, in particular, to a method and an apparatus for selecting features in a logical volume management environment. Still more particularly, the present invention provides a method and an apparatus to allow the user at boot time or at run time to select the features that should be enabled during the computer session.
2. Description of the Related Art
The Logical Volume Management System (LVMS) is a subsystem for on-line disk storage management that adds an additional layer between the device drivers and the block I/O interface in the kernel of the operating system to allow a logical view on storage. For systems without an LVMS, each of the partitions that is usable by the operating system is assigned a drive letter, such as xe2x80x9cC:xe2x80x9d or xe2x80x9cF:xe2x80x9d, producing a correlating drive letter for each partition on a disk in the computer system. The process which assigns these letters is commonly known. For systems with an LVMS, a drive letter may be mapped instead to a logical volume which may contain one or more partitions. The process by which partitions are combined into a single entity is known generically as xe2x80x9caggregation.xe2x80x9d
One of the unique features of this LVMS is the ability to accept plug-in modules. A plug-in module consists of executable code which can be loaded and run by the LVMS. Plug-in modules allow the capabilities of the LVMS to be expanded without having to alter the code of the LVMS itself. This simplifies development and maintenance while increasing the stability of the LVMS over time. The new capability provided by a plug-in module is also referred as feature. Note that the terms xe2x80x9cfeaturexe2x80x9d and xe2x80x9cplug-inxe2x80x9d are used interchangeably herein. An example of a feature would be non-local mirroring, whereby the contents of a volume are mirrored to a volume on another machine.
Features are plug-in components used by the LVMS to control how input/output (I/O) is performed to the partitions that comprise a logical volume. The input to a feature is the same in format and structure as the output from a feature. This allows the output from one feature to be used as the input to another, which, in turn, allows features to be stacked. Thus, multiple features may be applied to a volume. Every time the system boots, a feature stack will be constructed for each of the volumes in the system.
By default, when a volume is constructed, all features will be enabled and placed in the feature stack. Sometimes a feature will not be used and can be safely disabled. Therefore, it would be advantageous to have a method and an apparatus to allow the user to specify at boot time what features are to enabled in the logical volume management system.
A method and an apparatus for enabling and disabling features in a logical volume management environment is presented. This operation can be performed at boot time or at run time. The user is shown a list of features as well as the current state for each feature. If the feature is currently enabled, the user can select to disable the feature, provided this is a safe operation given the current features for the volume. If the feature is disabled, the user has the following choices: re-enable, disable and retain in the feature stack, disable and remove from the feature stack, and permanently remove the disabled feature from the volume.
Disabling or re-enabling features can be very useful to accommodate a changing operating environment. For example, the feature Volume Mirroring allows a replication of the volume at a remote site. If due to network difficulties that remote site becomes inaccessible, then this feature would have to be disabled. At a later time when the remote site becomes accessible again, the feature can be re-enabled.